Fotocromismo em filmes finos de óxidos de tungstênio de diferentes composições

Tungsten oxide thin films with three different compositions were deposited by reactive sputtering in an oxygen-argon plasma. In a system composed of a home made photochemical reactor coupled with an optic fiber spectrophotometer, the photochromic effect was studied in these oxide films as function of UV irradiation time, in ethanol, methanol and formaldehyde atmospheres. It was observed that the photochromic efficiency depends on the vapor chemical nature where the film is irradiated as well as the film composition. Kinetic analysis suggest that two kinds of optical absorption centers should respond by the photochromic effect in these films, one generated at film surface and other inside it, which one presenting a different time constant.

Synthesis, characterization and thermal behaviour of solid 2-methoxycinnamylidenepyruvate of some bivalent metal ions in CO2 and N2 atmospheres

Solid State M-2-MeO-CP compounds, where M stands for bivalent metals (Mn, Fe, Co, Ni, Cu and Zn) and 2-MeO-CP is 2-methoxycinnamylidenepyruvate, were synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), elemental analysis and complexometry were used to establish the stoichiometry and to study the thermal behaviour of these compounds in CO2 and N2 atmospheres. The results were consistent with the general formula: M(L)2∙H2O. In both atmospheres (CO2, N2) the thermal decomposition occurs in consecutive steps which are characteristic of each compound. For CO2 atmosphere the final residues were: Mn3O4, Fe3O4, Co3O4, NiO, Cu2O and ZnO, while under N2 atmosphere the thermal decomposition is still observed at 1000 º C.

Thermal behaviour of succinic acid, sodium succinate and its compounds with some bivalent transitions metal ions in dynamic N2 and CO2 atmospheres

Thermal stability and thermal decomposition of succinic acid, sodium succinate and its compounds with Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA) in nitrogen and carbon dioxide atmospheres and TG-FTIR in nitrogen atmosphere. On heating, in both atmospheres the succinic acid melt and evaporate, while for the sodium succinate the thermal decomposition occurs with the formation of sodium carbonate. For the transition metal succinates the final residue up to 1180 ºC in N2 atmosphere was a mixture of metal and metal oxide in no simple stoichiometric relation, except for Zn compound, where the residue was a small quantity of carbonaceous residue. For the CO2 atmosphere the final residue up to 980 ºC was: MnO, Fe3O4, CoO, ZnO and mixtures of Ni, NiO and Cu, Cu2O.

Conservative therapies for hemorrhagic radiation proctitis: a review

Chronic radiation proctitis represents a challenging condition seen with increased frequency due to the common use of radiation for treatment of pelvic cancer. Hemorrhagic radiation proctitis represents the most feared complication of chronic radiation proctitis. There is no consensus for the management of this condition despite the great number of clinical approaches and techniques that have been employed. Rectal resection represents an available option although associated with high morbidity and risk of permanent colostomy. The effectiveness of nonoperative approaches remains far from desirable, and hemorrhagic recurrence represents a major drawback that leads to a need for consecutive therapeutic sessions and combination of techniques. We conducted a critical review of published reports regarding conservative management of hemorrhagic chronic radiation proctitis. Although prospective randomized trials about hemorrhagic radiation proctitis are still lacking, there is enough evidence to conclude that topical formalin therapy and an endoscopic approach delivering an argon plasma coagulation represent available options associated with elevated effectiveness for interruption of rectal bleeding in patients with chronic radiation proctitis.

Use of legal reserve areas as geochemical background in hydrosedimentology studies¹

In hydrosedimentology studies the determination of the trace element concentrations at the study site is imperative, since this background can be used to assess the enrichment of sediments with these elements. This enrichment can be the result of the natural process of geological formation or of anthropogenic activities. In the latter case, guidelines are used to indicate the concentrations at which trace elements cause ecotoxicity effects on the environment. Thus, this study used legal reserve areas in the municipality of Toledo, PR, where natural forests are maintained, with no or minimal human interference to establish background levels. The results of atomic emission spectrometry with inductively coupled argon plasma showed that the legal reserves have lower levels of trace elements than other theoretical references, but equivalent concentrations to the safety levels recommended by international guidelines. It was concluded that determining values is fundamental to recommend this background as scientific database for research in the area of hydrosedimentology of this site and also as a way of environmental management of the watershed of this municipality.

Sensory characteristics of 'Douradão' peaches submitted to modified atmosphere packaging

The sensory, physical and chemical characteristics of 'Douradão' peaches cold stored in different modified atmosphere packaging (LDPE bags of 30, 50, 60, 75µm thickness) were studied. After 14, 21 and 28 days of cold storage (1 ± 1 ºC and 90 ± 5% RH), samples were withdrawn from MAP and kept during 4 days in ambient air for ripening. Descriptive terminology and sensory profile of the peaches were developed by methodology based on the Quantitative Descriptive Analysis (QDA). The assessors consensually defined the sensory descriptors, their respective reference materials and the descriptive evaluation ballot. Fourteen individuals were selected as judges based on their discrimination capacity and reproducibility. Seven descriptors were generated showing similarities and differences among the samples. The data were analysed by ANOVA, Tukey test and Principal Component Analysis (PCA). The atmospheres that developed inside the different packaging materials during cold storage differed significantly. The PCA showed that MA50 and MA60 treatments were more characterized by the fresh peach flavour, fresh appearance, juiciness and flesh firmness, and were effective for keeping good quality of 'Douradão' peaches during 28 d of cold storage. The Control and MA30 treatments were characterized by the mealiness, the MA75 treatment showed lower intensity for all attributes evaluated and they were ineffective to maintain good quality of the fruits during cold storage. Higher correlation coefficients (positive) were found between fresh appearance and flesh firmness (0.95), fresh appearance and juiciness (0.97), ratio and intensity of fresh peach smell (0.81), as well as higher correlation coefficients (negative) between Hue angle and intensity of yellow colour (-0.91), fresh appearance and mealiness (-0.92), juiciness and mealiness (-0.95), firmness and mealiness (-0.94).

Simulação da Química da Atmosfera Poluída por Automóveis Movidos a Álcool

Numerical modeling studies of urban atmospheres were performed with a photochemical box submodel which incorporates primary emission rates, temperature and solar irradiance rate coefficients. Actinic flux calculations were made for an appropriate latitude for Rio de Janeiro and initial concentrations and emission rates were taken from experimental data. The relative importance of individual reactions is discussed as well as the effect of enhanced aldehyde emissions from vehicles using ethanol and ethanol-containing fuel.

One pot obtention of a tetrabutylammonium hydroxide solution for ironporphyrin-OH- interaction studies in organic solvents

In this work we report the obtention of a tetrabutylammonium hydroxide (TBAOH) solution in acetonitrile in a one pot process in order to study the interaction ironporphyrinOH- in non-aqueous systems. All the reactions were carried out under dry argon atmosphere to prevent the contamination of the solution with CO2, which leads to the formation of (TBA)2CO3.

Metodologia para o crescimento de esferas monocristalinas de metais nobres

This paper describes in detail a technique employed to grow quasi-spherical single crystals of noble metals for electrochemical applications, using platinum as an example. The metal beads were formed by melting the extremity of a wire in an oxygen / butane flame. X-ray techniques were used to check the crystallization and to determine the orientation of the crystals. Treatment with a pure hydrogen flame followed by a cooling procedure in a hydrogen / argon atmosphere were used for conditioning the well-defined platinum single crystal surfaces. Finally, electrochemical characterization of the Pt(111), Pt(110) and Pt(100) surfaces was done in diluted sulfuric acid solution in the hydrogen adsorption / desorption potential region.

Geração eletroquímica do hidreto de selênio em sistema de injeção em fluxo com detecção por espectrometria de absorção atômica com chama Ar-Glp

This paper presents a system for electrochemical hydride generation using flow-injection and atomic absorption spectrometry to determine selenium in biological materials. The electrolytic cell was constructed by assembling two reservoirs, one for the sample and the other for the electrolytic solution separated by a Nafion membrane. Each compartment had a Pt electrode. The sample and electrolyte flow-rates, acidic media, and applied current were adjusted to attain the best analytical performance and ensure the membrane lifetime. The atomisation system used a T quartz tube in an air-LPG flame. The composition of the flame, the observation height, and the argon flow rate used to carry the hydrides were critically investigated. The system allowed to perform thirty determinations per hour with a detection limit of 10 mug L-1 of Se. Relative standard deviations were in general lower than 1.5% for a solution containing 20.0 and 34.0 mug L-1 of Se in a typical sample digest. Accuracy was assessed analysing the certified materials: rice flour (NIST-1568) from National Institute of Standard and Technology and dried fish (MA-A-2), whole animal blood (A-2/1974) from the International Atomic Energy Agency.

Um espectômetro de massas de tempo-de-vôo para o estudo da ionização de amostras gasosas por elétrons rápidos (0,5 - 1,0 keV)

A simple and inexpensive time-of-flight mass spectrometer, dedicated to the study of gas-phase ionization processes induced by high energy electrons (0.5 - 3.0 keV), is described. The spectrometer design is based on the Wiley-McLaren principle, with a total length of about 18 cm. As a demonstration of the performance of the apparatus, mass spectra for Ar, CH4, CO2, and SF6, obtained at 1 keV electron energy, are presented.

Contribuição ao estudo de uma metodologia alternativa para obtenção de dioxissulfeto de terras raras

In the last decade, many method has been developed to obtain oxysufides. However, theses materials were obtained by reaction involved gaseous toxics, CO, CS2, H2S and S. In the present work, the synthesis of lanthanum oxysufides actived by europium (III) through an alternative method has been made. This method involve the rare earth sulfate reduction under an atmosphere of argon contained 10% hydrogen using the thermogravimetric technique. The results showed the formation of the phase TR2O2S (TR = La and Eu) at temperatures which depend upon the heating rate, respectively 650 - 830ºC at 5ºC min-1 and 680 - 800ºC at 10ºC min-1. The oxysufides obtained are characterized by infrared spectroscopy. The method developed is more economic than the usual industrial methods and the environmental problems during the synthesis are also better controled.

Desenvolvimento de um micro-aquecedor para sistemas de análise química em fluxo: determinação espectrofotométrica de manganês em plantas

In this work a micro-heater device to be used as an integral part of the flow analysis manifold is described. The usefulness of the device was demonstrated using it in the development of a multicommutated flow analysis procedure for the spectrophotometric determination of manganese in plant digest. The method was based on the manganese oxidation by periodate in phosphoric acid medium to form the permanganate anion. The reaction development is dependent on the temperature and it was observed that at 25 °C a time interval of ca. 15 min was necessary for the reaction to attain equilibrium. Setting the temperature to 70 ºC, this time interval could be decreased to ca. 30 s. This condition was easily attained employing the proposed micro-heater device coupled to the manifold. The procedure was applied to manganese determination in soybean digests and results compared with those obtained by inductively coupled argon plasma optical emission spectrometry (ICP-OES). No significant difference at 90% confidence level was observed. A linear response for sample concentrations ranging from 5.0 to 30.00 mg L-1 Mn2+; a relative standard deviation of 1.3% (n = 6) for a typical sample containing 6.3 mg L-1 Mn2+; a sampling rate of 22 determinations per hour; a low reagent consumption, of 12.0 mg NaIO4 per determination; and a detection limit of 1.2 mg L-1 were achieved.

Espectroscopia de fotoelétrons de limiares de átomos e moléculas

A threshold photoelectron spectrometer applied to the study of atomic and molecular threshold photoionization processes is described. The spectrometer has been used in conjunction with a toroidal grating monochromator at the National Synchrotron Radiation Laboratory (LNLS), Brazil. It can be tuned to accept threshold electrons (< 20 meV) and work with a power resolution of 716 (~18 meV at 12 eV) with a high signal/noise ratio. The performance of this apparatus and some characteristics of the TGM (Toroidal Grating Monochromator) beam line of LNLS are described and discussed by means of argon, O2 and N2 threshold photoelectron spectra.

Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário

Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 ºC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 ºC in air atmosphere and at 894 ºC in nitrogen atmosphere.